This invention relates to the field of strength members and how to handle them, and more particularly to a device, method and coiled form of a strength member wherein the individual composite rods, or metal wires, or plastic fibers, or other materials in the strength member are bundled together in a generally parallel, untwisted and unspiraled orientation when the strength member follows along a generally straight path, but when the strength member is coiled, e.g., on a spool device, the strength member will be twisted along it longitudinal axis and the individual composite rods, or metal wires or plastic fibers forming the strength member will be in a twisted and spiraled orientation so that no undue stresses will be exerted on the coiled strength member. This twisting and spiraling will be more pronounced for rods, or wires, or fibers lying closer to the outer perimeter of the strength member and rods, or metal wires, or plastic fibers lying closer to a centerline of the strength member will be less twisted and spiraled or possible not twisted or spiraled. The invention is particularly well suited for strength members formed of composite rods, such as carbon fiber rods and composite rods formed of other materials such as glass fiber, synthetic fibers and the like, but can be used in forming long strength members of other materials, such as metal wire, plastics fibers, etc.
In the case of metal wires that wound on spools, these wires have a cast, or natural tendency to curve or twist along a clockwise or counterclockwise path, depending on whether the wire was wound clockwise or counterclockwise. Thus, when forming cable from these wires, manufacturers have either first straightened the wires before forming the cables, or have handled the natural cast, such as by balancing the casts of wires by arranging wires with opposite casts during the forming of the cable. Failure to deal with the natural case may result in cables that have a tendency to twist or coil in one direction or the other. Whether the metals wires are first straightened before being formed into cables, or are arranged with opposite casts, this does involves extra steps or extra attention being required during the manufacturing process. In contrast, in the case of composite rods, e.g., formed or carbon fibers and resins, these rods do not have a natural cast and thus they can be used to form cables without any straightening or consideration of whether the composite rods come prepared wound on spools in a clockwise or counterclockwise orientation.
For cables formed of metal wires in a generally parallel orientation, others, such as Durkee et al. (U.S. Pat. Nos. 3,526,570 and 3,659,633) have attempted to balance internal forces by bundling wires together that have opposite casts. Durkee et al. further disclose that by binding the bunched up wires by resilient securing material (i.e., flexible tape) at intervals of every few feet, the wires are allowed to bow out during the winding on a reel, which is said to relieve stress on the wires forming the cables. The individual wires making up the Durkee et al. cables would not be longitudinally or rotabably moveable relative to each other. Furthermore, the Durkee et al. methodology would not be applicable to cables in which the individual wires and strands are not allowed to bow out, such as cables constructed with inflexible binding and/or overwrapping material.
Long lengths of high strength cables are needed for a variety of applications, including lifting cables, long towing cables, mooring cables for offshore drilling platforms that can be located in waters that are many thousands of feet deep, and bridge tendons, to name just a few applications. In the past, these cables were made from materials such as steel, but more recently plastics and composite materials have been used. Composite materials have some advantage in high strength cable applications compared to metal and plastic, including an excellent strength to weight ratio and good corrosion resistance. For example, U.S. Pat. No. 7,137,617 for “Composite Tensioning Members and Method for Manufacturing Same” describes composite tension members made up of a plurality of composite fiber rods that are bundled together with the composite rods parallel to each other and unspiraled, unbraided and without stranding. More typically, composite cables have their composite rods arranged similarly to the wires and filaments in wire cables and ropes, namely, either they are formed by providing different layers of rods that are wound counter-helically relative to each other, as shown in prior art FIG. 1, which shall be referred to herein as stranded composite cables, or in a so-called six around one design, shown in prior art FIG. 2. One reason this is done is because the stranded composite cables in either prior art embodiment can be more readily bent and thereby wound around a spool for storage and handling. In contrast, composite cables with parallel composite rods, such as those disclosed in U.S. Pat. No. 7,137,617, are more difficult to handle and wind on a spool and the like. The machinery used to form very long lengths of larger diameter cables can be quite large and expensive due to the necessity of twisting together a number of very long rods, which rods themselves are spooled out from large spools, which number of large spools are themselves on a rotating carriage.
While stranded cables, whether formed of metal wire, plastics rods or fibers, or composite rods, can be more easily handled, there are some disadvantages with stranded cables. Stranded cables are made up of different overlapping layers of counter-helically wound rods, metal wires or plastic fibers, (as shown in FIGS. 1 and 2A.) In the cable with a six around one design of FIG. 2, there are many crossover points where crossing rods, metal wires, or plastic fibers contact each other. In the case of applications where such cables may sway, swing, or otherwise move, for example, as in mooring cables where they can be moved by ocean currents and the like, the effects of internal rubbing and abrasion of the composite rods, metal wires or plastic fibers in the crossover areas, for example, can weaken the cable. Moreover, in particular case of stranded composite cables, that are made of composite rods which are generally less stretchable than other materials, because of different rod lengths, some rods may carry more tension than other rods and this can result in less than optimal cable strength or failure of the cable. In contrast, cables where the individual composite rods, metal wires or plastic fibers are parallel to each other do not experience the problem of rubbing, and can be made so that each rod, metal wire or plastic fiber more evenly carries an equal tensile load, which helps in maximizing the strength of the cable. Moreover, due to tighter packing of the individual rods, or metal wires or plastic fibers in cables with a parallel rod, metal wire or plastic fiber configuration compared to counter-helically assembled or braided or six around one, for example, cables, the cable diameter of cables with a parallel composite rod, or metal wire, or plastic fiber configuration with the same number and size of composite rods, or metal wires, or plastic fibers can be made smaller in diameter. Thus, for a given size and weight and same material, a parallel composite rod, or metal wire, or plastic fiber cable will be lighter and have a smaller diameter, which means that a greater length of cable can be carried in the same space. As noted above, composite cables formed of parallel composite rods deliver excellent performance in terms of strength, weight, and space and is most ideal, although cables made of other materials are possible.
Accordingly, it would be beneficial to have a method and device for handling cables with parallel composite rods, or metal wires, or plastic fibers and also cables with parallel composite rods, metal wires, or plastic fibers provided on spools.